Update dependency docker/buildx to v0.21.3

Update docker/buildx from 0.21.2 to 0.21.3

Change-type: patch

Author: balena-renovate[bot]

.github/workflows/flowzone.yml

@@ -592,7 +592,7 @@
     uses: docker/setup-buildx-action@b5ca514318bd6ebac0fb2aedd5d36ec1b5c232a2 # v3.10.0
     env:
       # renovate: datasource=github-releases depName=docker/buildx
-      BUILDX_VERSION: v0.21.2
+      BUILDX_VERSION: v0.21.3
     with:
       driver-opts: network=host
       install: true
@@ -2147,7 +2147,7 @@ jobs:
           # is created without the "default" target.
           # See https://github.com/docker/buildx/issues/2859
           # renovate: datasource=github-releases depName=docker/buildx
-          BUILDX_VERSION: v0.21.2
+          BUILDX_VERSION: v0.21.3
 
       # generate a custom bake json string from the provided bake targets and any discovered bake files
       # https://docs.docker.com/build/customize/bake/file-definition/#json-definition